The Plastic Bag Experiment is awesome! It’s doesn’t take a lot of time and chances are good that you have all the “ingredients” around the house. I did this with my three and a half year old, and it would be relevant for preschoolers and elementary-age children.

The idea that we’re testing here is what will happen if we poke a sharp pencil through a plastic bag of water. Will the water leak through the holes? Will the water spill out? Or will the bag reseal around the pencils, keeping the water inside?

When my 3-year old daughter (N) and I tried this out, we worked with the question, “what will happen if we poke pencils into a bag full of water?” That seemed more age-appropriate and tangible for her.

Supplies

Zip-up Bag

Water

Sharpened Pencils

We filled a zip-up bag about half-way with water and sealed it up. I held the bag high over a sink and N poked the pencils straight through the bag, from one side to the other. This is where my fancy photography skills come into play, holding the bag with one hand and snapping a photo with the other. Are you impressed?

Make sure that the pencil doesn’t keep traveling through the bag or you’ll have water leaks.

Keep adding pencils until you’ve had enough. Before removing the pencils, take a moment to talk about what you see. When the pencil goes into the bag, the bag seems to magically seal itself around the pencil.

When you’re done, remove the pencils over a sink.

The Science Behind the Experiment

Plastic bags are made out of polymers, chains of molecules that are flexible and give the bag its stretchiness. When the sharp pencil pokes through the bag, the stretchy plastic hugs around the pencil, creating a watertight seal around the pencil…and the bag doesn’t leak.

More Science Projects for Kids

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I’m a recycler at heart, so projects that incorporate found materials (such as plastic lunch bags and wrapping paper) speak to my soul and my aesthetic. This is one such project. And it was also a true experiment as I’d never done this before and wasn’t at all sure how it would turn out. I love that! I borrowed this idea from MaryAnn Kohl’s Art with Anything.

We began by filling plastic lunch bags with odds and ends: stickers, cut-up pieces of old art, and wrapping paper. While we worked on this right after breakfast, which sort of explains the pajamas, my child would live in her pj’s if she could. She seems happiest jumping around the playground, but I think she may be a little cozy homebody at heart.

Once the bag was ready, we placed it between two pieces of aluminum foil…

and then ironed it flat.

After letting it cool for a minute, we peeled the foil apart to reveal our “laminated” art. While difficult to see in the photos, the heated texture of the plastic turned out mottled and bumpy. N wanted to open the bag after we heated it, which led to a nice convo about how the bag melted.

Hey, that was fun. Let’s do that again!

We made three of these altogether — two were by N and the third was a collaboration (a new word we’re working on!). We made the top two with sandwich baggies and the bottom with a ziplock bag — each worked equally well. This turned out to be fun and educational on a number of fronts:

Exploring Volume: My child adores filling bags with things. If she had a mountain of bags to fill while wearing her pajamas all day, she’d be in her own little piece of heaven. If your child likes to fill bags too, this project could be for you!

Problem-solving, creative thinking, and exploration: She could choose from an assortment of materials, and was thoughtful about which items to fill the bags with.

Practicing a skill: For us this was cutting with Scissors. She’s been practicing this for a while, but has recently hit her cutting stride. So for us, a good half hour was spent on just cutting up wrapping paper.